The present invention relates to a scratch resistant acoustical coating for an acoustical panel and more particularly to a scratch resistant discontinuous primer coating for an acoustical panel.
As the service sector of the economy grows, more and more workers find themselves in offices rather than in manufacturing facilities. The need for flexible, reconfigurable space has resulted in open plan workspaces, large rooms with reduced height, moveable partitions and suspended ceiling systems. Workstation density is also increasing, with more workers occupying a given physical space. Additionally, speakerphones, conferencing technologies, and multimedia computers with large, sound reflecting screens and voice input tend to increase the noise level of the workplace.
In closed spaces, particularly in office and meeting room settings, speech intelligibility and acoustic performance are determined by a variety of factors, including room shape, furnishings, number of occupants, and especially floor, wall and ceiling treatments. This acoustic environment determines how much sound intrusion occurs as well as the affect on listeners by extraneous noise.
Such acoustical environments are typically modified using acoustical surfaces having sound absorbing qualities. A common sound absorbing surface in a building is found in the acoustic panels used to cover the ceiling, wall or other surface. Acoustic panels are generally composed of porous layers of mineral or vegetable fibers bonded together with non-thermoplastic resins. The panels may also be composed of glass fibers. Acoustic panels are typically provided with substantial porosity to absorb sound waves emanating from within a room. Porosity is evidenced on the surface of the acoustic panels by the presence of small recesses or pores of varying diameter which permit sound waves to enter the material and be dispersed. Additionally, the panels may be acoustically enhanced by mechanical texturing. This texturing produces small holes in the surface of the panel to admit sound which is either dissipated in the interior of the panel or transmitted through the panel.
In the manufacture of acoustical ceiling panels, it is usually necessary to apply colored coatings to the surface of acoustical ceiling panels. Aesthetic finishes are achieved by a combination of texturing and painting the surface of the panel. Achieving a desired coloration of the panel material may require the application of several layers of paint or pigmentation and a primer layer to provide a standard base color and adhesion for additional layers.
The raw materials comprising acoustical panels typically have poor durability and scratch resistance leading to marring of the finished product. To prevent such marring, a coating can be added to provide increased durability to the surface of the panel. Coatings can also be added to limit flammability and flame spread.
Furthermore, moisture and high-humidity can cause a weakening of the material comprising acoustical ceiling panels. This may cause a panel to sag in the middle. Coating one or both surfaces of a panel can both reduce the penetration of moisture into the panel, and impart additional tensile strength to reduce sagging.
Unfortunately, coatings applied to the room-side surface of the panel tend to clog the pores or holes that are necessary for good acoustical performance, thus impairing the acoustical performance of the panel.
Thus, there is a need for a coating that leaves open the sound absorbing pores of an acoustical panel such that there is no appreciable effect on the acoustic performance of a panel. Additionally, there is needed a coating capable of providing a scratch resistant surface to a panel while also providing improved adhesion for applied coatings.
The present invention provides for both a composition and method for producing a scratch resistant discontinuous primer coating on an acoustical panel. Acoustical panels can be any manufactured surface having sound attenuating properties, such as acoustical ceiling tiles, room partitions or highway barriers.
The applied coating primarily comprises binder, filler and mica and is typically applied as a spray. The coating can be characterized as a discontinuous film, whereby sound can pass through the coating to the panel for attenuating sound.
The coating provides a durable finish and increased handleability along with color without compromising the acoustical performance of the substrate. Handleability is an important aspect of panel durability. Related to handleability are the metrics of Modulus of Rupture (MOR) and Modulus of Elongation (MOE), which relate to the structural integrity of a material, which is also increased by the coating of the present invention.
In more detail, the discontinuous acoustical surface coating of the present invention on a dry weight percent basis comprises about 4 to about 80% mica, about 10 to about 45% binder; and about 10 to about 86% filler. The filler is typically clay and the binder is typically starch.
The process primarily comprises combining and mixing the dry components of filler, binder and mica and then combining the same with water and mixing to create an aqueous mix that can be applied to the acoustical panel and dried.
The method for creating a discontinuous acoustical surface coating comprises the steps of combining and mixing mica, filler and binder to form a dry mix which comprises about 4 to about 80% mica, about 10 to about 45% binder, about 10 to about 86% filler. Then the dry mix can be combined and mixed with water to form a wet mixture that is then sprayed onto the panel to form a coated panel. The components may also be mixed together in one step and then sprayed onto the coated panel. The coated panel is either air dried or heated in an oven.
The present invention provides for both a composition and method for producing a scratch resistant coating applied to an acoustical panel. The coating primarily comprises binder, filler and mica and is typically applied as a spray. The coating can be characterized as a discontinuous film whereby sound can pass through the coating to the panel for attenuating sound. Discontinuity is provided by pores formed by the filler component. The coating is thus enabled to provide a finish and color without compromising the acoustical performance of the substrate.
Additionally, the discontinuous acoustical coating primes the surface of the panel. As a primer, the coating adds adhesion between the substrate and successive layers.
In an embodiment, the composition of the coating comprises mica, clay as a filler and starch as the binder. In the coating, mica can comprise from about 4% to about 80% by dry weight of the coating and alternatively between about 4% to 25% by dry weight. In one embodiment, mica comprises about 8% by weight of the coating. Experimentation has indicated that as mica is added in amounts over 80%, the probability of sound permeability of the resulting coating being decreases to an NRC of less than 0.50 at the lower stated application rates increases.
Clay or filler can comprise between about 10% to 86% by dry weight of the coating and alternatively between about 10% to 55% by weight. In one embodiment, the filler comprises about 77% by weight of the coating. The filler is substantially responsible for creating the voids within the coating which allow sound to pass though the coating to the panel where it is dissipated.
Starch or binder can comprise between about 10% to about 45% by weight of the coating and alternatively between 10% to 30% by weight. In one embodiment, starch can comprise about 15% by weight of the coating. The binder or starch is combined with the mica to create the primer coating with significantly improved xe2x80x9cfinger scratchxe2x80x9d results (approximately one to two rating points).
An example of a mica comprising the coating includes Mica 325, available from Franklin Industrial Minerals, of King Mountain, N.C. The average particle size of the mica can range from 20 to 100 150 microns. Additionally, the mica can be surface treated to improve the adhesion of mica to polar substrates. Such surface treatments can include silanes or siloxanes and mixes thereof such as aminopropyltrimethoxysilane and gamma-glycidoxypropyltrimethoxysilane.
An exemplary starch for inclusion within the coating composition includes a cold-dissolvable starch such as Mira-Cap, available from AG Staley Co. of Decatur, Ill. An exemplary material for clay is EG-44 clay, available from Thiele Kaolin Co. of Sanderville, Ga.
Alternative binders may be substituted for starch in whole or in part in the coating composition. Such binders may include polyacrylic acid and its copolymers, protein/epoxy combinations, carboxylated polymer/epoxy combinations and mixtures thereof of such binders. Example polyacrylic acids include Alcosperse 404, available from Alco Chemical of Chattanooga, Tenn. Example protein/epoxy combinations include proteins such as ProCote 184A, available from Protein Technologies of St. Louis, Mo., and epoxies such as Epi-Rez 3522-w-60 from Shell Chemical of Houston, Tex. Example carboxylated polymers/epoxies include Rosin Resin Pentalyn 856, available from Hercules Corp. of Wilmington, Del., and epoxies such as Epi-Rez 3522-w-60 from Shell Chemical of Houston, Tex.
The dry ingredients are combined with a solvent, preferably water, to form a wet mixture. Typically, water can comprise approximately 25% to 90% of the wet mixture and alternatively water can comprise between 43% to 50% of the wet mixture. In one embodiment, water comprises about 46.5% of the wet mixture and the dry ingredients about 53.5% to provide a desired consistency for spraying onto panels.
To prepare a wet mixture that yields a sprayable material that dries with the desired characteristics, additional ingredients, well known in the art, can be utilized. Dispersants, such as Aquaquest 2120, available from GeoSpecialty Chemicals of Charlotte, N.C., can be utilized to aid in the dispersal of included ingredients. Defoamers, such as Tego Foamex 1488, available from Tego Chemie Service, GmbH-Essen Germany, can be utilized to reduce foaming during the mixing process.
In an alternative embodiment, the final wet mixture may have additional ingredients to improve usability and other characteristics not necessarily related to scratch resistance or durability of the coating. For example, in one alternative embodiment, a biocide such as Metasol D3T-A, available from Calgon Corp. of Pittsburgh, Pa., may be added in small amounts (typically less than 1% by weight) to impair bacterial growth. Additionally, a wetting agent such as Tergitol TMN-6, available from Union Carbide, of Danbury, Conn., may be added to improve the wetting of the panel surface and to improve adhesion of the coating.
In an additional embodiment, large, medium, or small particle fillers may be added, including calcium carbonate, limestone, titanium dioxide, sand, barium sulfate, other clays, dolomite, silica, talc, perlite, polymers, gypsum, calcite, aluminum trihydrate, pigments, zinc oxide, and zinc sulfate.
The present process primarily comprises combining and mixing the dry components of filler, binder and mica and then combining the same with water and mixing to create an aqueous mix that can be applied to the acoustical panel. Of course the dry ingredients can be added as a slurry, or in the case of the binder, as a liquid. Typically, the aqueous mix has a viscosity suitable for application using conventional spraying techniques. After the aqueous mix is applied to the panel, it is then dried on the panel to form a scratch resistant coating.
Combining and mixing the dry components typically occurs in a mixer capable of mixing both the dry components and wet components, wherein the process can be a batch or continuous process. The components defined as dry components are labeled such for convenience and it is not implied that such components need to be added dry. For example, clay or filler is commonly added as a slurry and polymer binders are often added as emulsions.
The step of adding a liquid to the dry components is described as a separate step for clarity and it is not meant to limit the present process to such a distinctive step separate from the combining of the other components. Water can be added and mixed simultaneously with the other components of the coating or separately.
The step of applying the coating to the panel is typically done by spraying the wet mixture onto the panel. Other application techniques may also be used, such as the use of rollers or brushes, or dipping.
The step of drying the coating to the panel can either be done at room temperature or at elevated temperatures, such as those found in an oven. When protein/epoxy combinations and carboxylated polymer/epoxy combinations are used as a binder there is a requirement for elevated temperatures. Protein/epoxy combinations typically require that the coated panel be dried at temperatures between 300xc2x0 F. and 500xc2x0 F. Carboxylated polymer/epoxy combinations typically require that the coated panel be dried at temperatures between the same temperatures as above.